Hepatitis B is an infectious disease which is caused by hepatitis B virus (HBV), mainly causes hepatic lesions and can cause a variety of organ damages. The harm of the hepatitis B is most serious in various types of existing viral hepatitis, in the acute viral hepatitis, the hepatitis B accounts for about 25% (wt %), and in the chronic hepatitis, the hepatitis B accounts for 80%-90% (wt %). The course of the hepatitis B is prolonged and the hepatitis B is easily transformed into chronic hepatitis, cirrhosis and liver cancer. The endemic areas of the disease spread all over the world, although the HBV infection is prevented by large-area inoculation of hepatitis B vaccines, the prevention and the treatment for current patients with the hepatitis B and HBsAg carriers are still arduous in the following several tens of years.
It is reported in Chinese patent CN1493301A that the 6-methoxy-2′,3′-dideoxyguanosine is a nucleoside analogue with anti-HBV activity and can fight against the hepatitis B virus, prevent the production of drug-resistant strains, prevent the liver cancer and fight against lamivudine-resistant virus mutants. In addition, inventors further found that the 6-methoxy-2′,3′-dideoxyguanosine plays the role of fighting against the HIV (Human Immunodeficiency Virus) through the experimental study. The 6-methoxy-2′,3′-dideoxyguanosine has the following structural formula:

The 6-methoxy-2′,3′-dideoxyguanosine can be rapidly metabolized in plasma to 2′,3′-dideoxyguanosine (ddG) which is a prodrug of ddG. The ddG can be phosphorylated to an active triphosphate ddGTP in cells, and the DNA replication can be suppressed through the combination with a polymerase, thereby resulting in the stop of the DNA chain synthesis. Although the 6-methoxy-2′,3′-dideoxyguanosine can suppress the DNA replication, the DNA polymerase and the polymerase activity of a reverse transcriptase still exist. Meanwhile, compared with a dideoxycytidine triphosphate (ddCTP), although the ddGTP is effective for the chain suspension of the DNA replication, the experimental study shows that the ddGTP can selectively compete with the ddCTP for suppressing the DHBV DNA replication.
Chinese patent CN14156222A and Robins M. J. (J. Org. Chem. 1995, 60(24), 7902-7908), etc. disclose the method for preparing the 6-methoxy-2′,3′-dideoxyguanosine. The 6-methoxy-2′,3′-dideoxyguanosine obtained by the method disclosed by the forementioned documents is a final product which is finally prepared by the recrystallization method and is in line with the pharmaceutically required purity generally. The water content of the 6-methoxy-2′,3′-dideoxyguanosine product prepared by the prior publication documents is not higher than 4% (wt %). However, the inventors found that when the water content of the 6-methoxy-2′,3′-dideoxyguanosine obtained by recrystallization in the presence of a variety of solvents and under a variety of conditions (such as temperature and devitrification speed) is lower than 6%, the 6-methoxy-2′,3′-dideoxyguanosine is very easy to absorb moisture and be blocked under the general conditions, thereby changing the character thereof and bringing about great inconvenience for transportation, production and pharmaceutical preparations.